Despite the fact that many different nano scale materials are already in use in consumer products, the ability to determine the specific toxicity of many of these materials is still limited when compared to other materials. For example, the initial discovery of Buckminster fullerene, C60 (commonly called bucky balls), described in Kroto H. W., Heath J. R., O'Brien S. C., Curl R. F. and Smally R. E. (1985). Nature 318 162, stimulated a great deal of research. However, much of the work related to aerosol generation of bucky balls (the form typically used for toxicity studies) was directed towards characterizing various properties such as phase, crystallinity, reactivity, geometry, physical and chemical properties. Such studies include, for example, that described in David E. Mccready and Mikhail S. Alnajjar (1993). “Powder data for Buckminster fullerene, C60” Powder Diffraction. 9(2) June 1994. Some of the previous studies to generate C60 aerosols include nebulizing a solution of C60 in toluene and subsequent vaporization and condensation of the aerosol stream to break the huge aggregates. One such study is described in J. Jouttsensaari, P. Ahonen, U. Tapper, E. I. Kauppinen, J. Laurila and V. T. Kuokkala “Generation of nano phase fullerene particles via aerosol routes” Synthetic Metals 77 (1996) 85-88. Such approaches are generally undesirable for generating aerosols for inhalation studies, as the toluene contained within the aerosolized materials is incompatible with inhalation studies.
Despite limited study of the toxicity of these nano scale materials, there are several specific reasons that support the suspicion that toxicity may peculiar to nano scale materials. For example, in Kreuter, J. 2001 “Nanoparticulate systems for brain delivery of drugs” Adv Drug Delivery Rev 47:65-81, it was shown that nano materials can access regions of the body that are not open to larger particles, and that there is evidence that nano particles will be capable of crossing the blood-brain barrier, and leaking out of capillaries. Nano scale materials may enter via mechanisms that are distinct from larger particles and may escape common clearance pathways for particulate matter. Also, nano materials have a very high surface to volume ratios; their high surface-free energy leads to facile adsorption of molecular contaminants, offering a potential route for such molecular contaminants into regions of the body not normally accessible. Accordingly, as will be appreciated by those having ordinary skill in the art, methods and apparatus suitable for generating nano-sized particles would thus be useful not only for inhalation studies, but also for any application where these nano-sized particles, and substances contained within them or chemically bonded to them, are introduced into regions of the body not readily accessible by other means. Accordingly, there is a need in the art for methods and apparatus suitable for generating nano-sized particles.